82 SECTIONAL ADDRESSES. 



But, in addition to these brief and local minglings of Avonian and 

 Lancastrian, evidence is accumulating to show that the upper Yoredalian 

 was synchronous with the lower Lancastrian ; in other words, that the 

 Yoredale type of deposit was being laid down in parts of Yorkshire while 

 Mr. Bisat's lower E beds were accumulating elsewhere. If this is established 

 it will mean that the upper Yoredalian is not Avonian at all, but Lancastrian, 

 and will render it more possible to regard the D, and D^p beds of the 

 Midlands and South as the time equivalent of the Yoredalian, reduced as 

 it will then be by the separation of its Lancastrian portion. 



The Dibunophyllum Zone (sensu lato) and its equivalents in the 



North of England. 



While, as regards the -pie-Dibunophyllum beds, the calcareous phases 

 in England and Wales are far more important than any other phase, when 

 we come to the Dibunophyllum beds this is not so, at any rate in the North 

 of England, where rocks predominantly shaly are fully as important as 

 those of the calcareous phases. 



While, too, in the South-western Province the difficulties of correla- 

 tion are comparatively slight, when we reach Yorkshire this is far from 

 being the case, and much difference of opinion exists even on major 

 questions of classification and correlation. To clear up these difficulties, 

 a Committee of this Association was appointed, and a report, mainly drawn 

 up by Mr. R. G. S. Hudson, the secretary, was issued at the Southampton 

 Meeting last year. Largely owing to the still imperfect state of our 

 knowledge, it proved impossible to obtain general agreement among the 

 members of the Committee, and two sub-reports dissenting from certain 

 parts of the main report are appended. These differences of opinion are 

 partly on questions of terminology, partly as to the correlation and sub- 

 division of the strata. The various proposals will be found in the Report 

 of the British Association Committee, and in Mr. Cosmo Johns' paper in 

 the Naturalist of July 1926. Little is to be gained by recapitulating 

 these in detail. The main thing to strive for is to avoid increasing and, 

 if possible, to lessen the existing confusion. Some of the chief questions 

 at issue are : — 



(1) As regards ' Yoredalian.' Is the term to be used ? If so, what are 

 its limits to be ? Is it to be (a) a major division of the Lower Carboniferous 

 equivalent to the Tournaisian and Visean, or (6) a subdivision of the 

 Visean equivalent to the D zone and S zone, or (c) an alternative name 

 for the highest part of the D zone, equivalent in fact to an extended D., ? 



(2) Is it desirable to adopt the zone (of Orionastrcea philUpsi) as 

 proposed by the B.A. Committee 1 



(3) What are the best levels to take for delimiting Dj and D.j ? 



(4) If the term Yoredalian is adopted, is D3 also necessary ? or may D., 

 as far as the northern development is concerned be merged in Yore- 

 dalian ? 



We have in the first place Phillips' main division into Great Scar 

 Limestone and Yoredale Series, based on obvious differences conspicuous 

 throughout the greater part of the area, though, as he recognised, this is 

 not the case in part of the south-eastern section, owing to the lower 

 members of the Yoredale series being represented by massive limestone. 



